UMTS (Universal Mobile Telecommunications System) networks are making the most of the features of a W-CDMA (Wideband Code Division Multiple Access) based system by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access) aiming at improving frequency utilization efficiency and improving data rates. For these UMTS networks, Long Term Evolution (LTE) is under study for the purpose of realizing higher data rates and lower delay or the like (e.g., see Non-Patent Literature 1).
Third-generation systems can generally realize a transmission rate on the order of maximum 2 Mbps on the downlink using a 5-MHz fixed band. On the other hand, LTE systems can realize a transmission rate of maximum 300 Mbps on the downlink and on the order of 75 Mbps on the uplink using a variable band of 1.4 MHz to 20 MHz. In the UMTS networks, systems as successors of LTE are also under study for the purpose of realizing a wider band and higher speed (e.g., LTE Advanced (LTE-A)). For example, LTE-A is scheduled to expand 20 MHz which is a maximum system band of the LTE specification to the order of 100 MHz.
In an LTE system, a radio base station apparatus (BS: Base Station) measures uplink channel quality based on SRS (Sounding Reference Signal) for measuring channel quality transmitted from a mobile terminal apparatus (UE: User Equipment), performs scheduling for the mobile terminal apparatus to transmit a data channel signal (PUSCH: Physical Uplink Shared CHannel) and instructs the scheduling using a PDCCH (Physical Downlink Control CHannel). In Release 8 LTE, SRS is multiplexed with a final symbol of a subframe constituting an uplink radio frame and periodically transmitted from the mobile terminal apparatus to the radio base station apparatus.